docs: def validate_value(self, value):
          """Validate provided record is a part of the appropriate target app for the field"""
          if value not in (None, self._unset):
  
              super(ReferenceField, self).validate_value(value)
  
              if value.app != self.target_app:
                  raise ValidationError(
                      self.record,
                      "Reference field '{}' has target app '{}', cannot reference record '{}' from app '{}'".format(
                          self.name,
                          self.target_app,
                          value,
                          value.app
                      )
                  )